The present invention relates to a belt tension measuring apparatus.
In many belt drive system applications, it is important to optimize belt tension. The purpose of a belt tensioner is to maintain a substantially constant tension in a drive belt. In most applications, the belt connects stationary pulleys. Hence, belt tension can be set by affixing one pulley to a mount having an adjustable linkage to a fixed mounting surface. Automobile engine belts are common examples of this type of system.
In typical power transmission arrangements, a belt is spanned over and around one or more pulleys. Conventionally, to measure a tension of the belt, the belt is pushed downwardly under a predetermined pressure applied by means of a pressure gauge (or manometer) disposed so as to bear against the belt at a predetermined position thereof, whereby the belt is deflected downwardly by a predetermined distance or deflection. The pressure applied to the belt at that time point is measured by using the pressure gauge itself. Mechanical devices for measuring drive belt tension thus are purely mechanical and clamp on to a short section of the belt and predict tension either by applying a known force and measuring belt deflection, or by applying a known deflection and measuring force. Through tests carried out in the laboratory using a tensile testing machine we have shown that these devices give both poor accuracy and poor repeatability of results. Measuring errors of up to 60% can occur in a random manner. One of the reasons why error occurs is that, if the belt slips by even a small amount where it is clamped, this will significantly alter the force/deflection characteristic.
As discussed in U.S. Pat. No. 5,877,431, tension measurement for a flexible member such as the belt employed in association with a power transmission such as that of the engine of a motor vehicle, can use a string tension measuring technique adopted in a process for tuning a string instrument. FIG. 1 is a block diagram showing schematically an apparatus for measuring a string tension of a musical instrument. A sound generated by vibration of a string of concern is collected by a microphone 1 which converts the sound as caught into an electric acoustic signal which is then outputted to a signal processing unit 2 which serves for processing the acoustic signal supplied from the microphone 1 to thereby measure a natural oscillation or vibration frequency of the string and display the natural (vibration) frequency (also known as the characteristic or proper frequency) in the form of numerical values. To this end, the signal processing unit 2 is comprised of an input signal shaping circuit 21 for shaping waveform of the acoustic signal inputted from the microphone 1 to thereby eliminate noise components, a frequency counter 22 for sampling or quantizing the acoustic signal outputted from the input signal shaping circuit 21 to thereby convert the input signal into a digital signal for the purpose of frequency measurement thereof, a CPU (abbreviation of Central Processing Unit) 23 for processing the frequency data as measured for the numerical display thereof, and a display drive circuit 25 for displaying the frequency data as processed on a display device 24. When a string of a musical instrument such as violin is caused to vibrate under frictional sweeping of a bow, the string vibrates at a frequency intrinsic to the string, whereby a vibration sound is generated, which sound is collected by the microphone 1 to be converted into an electrical acoustic signal. In the signal processing unit 2, the acoustic signal undergoes the waveform shaping processing affected by the input signal shaping circuit 21 for the purpose of noise elimination. The acoustic signal outputted from the signal input shaping circuit 21 is then inputted to the frequency counter 22 to be converted into a corresponding digital signal, from which frequency data is generated by counting the pulses contained in the digital signal. The frequency data is then processed by the CPU 23 to a form suited for a numerical display to be subsequently displayed on the display device 24.
The technique for measuring the natural vibration frequency of the of the string of a musical instrument has been applied to measurement of the natural vibration of a belt employed in the engine for the motor vehicle by collecting the vibration sound generated by the belt by applying a vibration and collecting it by the microphone 1 and processing the acoustic signal by the signal processing unit 2 for displaying the natural vibration frequency of the belt and/or the tension arithmetically determined on the natural vibration frequency in terms of a numerical value. As discussed in U.S. Pat. No. 5,877,431, the apparatus for measuring a tension of a belt in a spanned state includes a vibration detector for detecting a vibration of the belt, a vibration frequency arithmetic unit for arithmetically determining a vibration frequency on the basis of the vibration as detected, and a tester equipped with a display device. The tester includes an information processor for arithmetically determining a tension of the belt on the basis of the vibration frequency supplied from the vibration frequency arithmetic unit and information about the belt read out from a storage medium, and the display device for displaying the result of the arithmetic operation performed by the information processing means. The tension measuring apparatus is then used for detection of a tension of a belt of a car belt transmission.